1. Field of the Invention
This application was filed claiming Paris Convention priority of Japanese Patent Application No. 2007-207649, the entire content of which is herein incorporated by reference.
The present invention relates to a light diffuser plate, and more particularly to a light diffuser plate which is preferably used in a state of being incorporated in a transmissive image display.
2. Description of the Related Art
As shown in FIG. 1, a light diffuser plate (1) is widely used in a state of being incorporated in a surface light source (3) constituting a transmissive image display (2) [Patent Document 1: Japanese Unexamined Patent Publication (Kokai) No.2004-170937]. The transmissive image display (2) shown in FIG. 1 comprises the surface light source (3) and a transmissive image display panel (4) disposed at the front side of the surface light source. The surface light source (3) comprises the light diffuser plate (1) and plural light sources (5) disposed at the back side of the light diffuser plate (1). In the transmissive image display (2), incident light (L0) incident upon the back side of the light diffuser plate (1) from the light source (5) is diffused while transmitting into the light diffuser plate (1), and then diffused light (L1) is emitted from the front side and illuminates the transmissive image display panel (4). As the light diffuser plate (1), a light diffuser plate comprising a colorless and transparent resin having a light diffuser dispersed therein is widely used since a comparatively light weight can be achieved even if the size of an image plane increases.
The light diffuser plate (1) is preferably a light diffuser plate which can illuminate the transmissive image display panel (4) more brightly.
The present inventors have intensively studied so as to develop a light diffuser plate which can illuminate the front side more brightly when used in a state of being incorporated in a surface light source, and found the followings. That is, even if a transparent resin constituting the above light diffuser plate is seen as colorless and transparent with the naked eye, it is usual that a light transmittance [T365] at a wavelength of 365 nm is slightly lower than a light transmittance [T600] at a wavelength of 600 nm, which may result from impurities incorporated during the manufacturing process. Low light transmittance [T365] at a wavelength of 365 nm possibly exerts an influence on the diffusion of transmitted light due to the light diffuser. This leads to an influence on the brightness of the illumination and thus, the present invention has been completed.